1. Field of the Invention
The present invention relate to torque wrenches and ratchet drive arrangements, such as used in socket wrenches and the like.
2. Description of the Prior Art
In conventional torque wrench designs a torque wrench handle includes a member called a hinge, which has an elongated portion extending within a sleevelike handle and terminating at one end beyond the handle in a generally annular ratchet ring. The ratchet ring typically has a generally circular aperture therethrough with radially interiorally directed ratchet teeth defined in the wall thereof. A work engaging element, sometimes called a workpiece or driver is provided and extends into the ratchet ring cavity. The workpiece includes a square lug for engaging a socket wrench or the like protruding outward beyond the ratchet ring and perpendicular thereto along the workpiece axis. The lug normally depends from a disk shaped mounting flange that seats against the ratchet ring in sliding contact therewith. Extending from the disk shaped mounting flange opposite the lug is a configured bearing post which extends the width of the ratchet ring to occupy a major portion of the volume defined by the cavity therein. The bearing post is formed with a chordal shoulder which, together with the toothed interior ratchet ring wall, define a segmental section of the cavity volume not occupied by the pedestal structure. Within this segmental cavity a pawl is disposed to selectively effectuate engagement of the workpiece with the ratchet ring during a rotational stroke of the hinge in one direction, and to allow the ratchet ring to rotate relative to the work head on the return stroke of the hinge. A control member, typically an index ring is positioned over the ratchet ring and carries a depending finger parallel to the axis of work head rotation to manipulate the pawl into position to engage the work head for rotation with the ratchet ring in either direction of rotation, or to disengage it entirely. The user is thereby able to control the direction in which the hinge can be rotated to apply power to the workpiece.
In conventional torque wrenches the pawl is typically formed with flat upper and lower surfaces and with a dog, catch or teeth directed outwardly from the axis of work head rotation for engagement with the ratchet ring.
The pawl is conventionally constrained from movement in the direction of work head rotation and restrained from tipping or tilting within the cavity in which it is held by the snugness of fit of the flat upper and lower surfaces against the disk shaped flange of the work head on the one side and against the interior surface of a cap over the index ring on the other side. Heretofore, failures in a torque wrench mechanism typically occur due to fracture and shearing of teeth in the pawl or in the ratchet ring. Ideally the flat surfaces of the pawl lie in parallel planes perpendicular to the axis of work head rotation and form a very snug fit with the capturing elements to prevent misalignment. However, the closeness of this fit is governed by the sum of production tolerances of the work head, the hinge (including the dimensions of the ratchet ring) the indexing ring, the cap and the pawl. In conventional articles, not even a worst case condition of production tolerances is required to produce a significant gap between the pawl and the confining surfaces parallel to the plane of the ratchet ring. As a consequence, in conventional torque wrenches, the pawl is at the mercy of random initial contact points when it is brought by movement of the hinge to bear against the ratchet ring and the pedestal of the work head. This frequently results in the premature failure of both the pawl and the hinge.
The situation is aggravated even further when the torque wrench operator pulls on the handle at an angle. This is a very frequent occurrence in operating a torque wrench, or a socket wrench, for example, to loosen and tighten nuts and bolts in spaces having limited clearance and leverage room. In operating a torque wrench under such conditions the hinge axis may be canted significantly (2 degrees for example) relative to its normal disposition perpendicular to the axis of rotation of the work head. As torque is applied through the hinge, the initial contact between the teeth of the pawl and the teeth of the ratchet ring is at the extreme edge of the pawl. When torque is applied the pawl rotates until it is restrained by the work head and its related parts. Because of the unsymmetric load applied to the pawl, the teeth of the pawl are held in misalignment with the teeth of the ratchet ring. The fact of this effect can be seen since the failure of the pawl or ratchet ring teeth shows a progressive shear. The shear starts at one edge of a tooth and proceeds to approximately two thirds of the tooth width.